Damage to the joints of the human body, due to arthritis, other degenerative diseases or trauma, often results in the need to replace the joint with a prosthetic device. In the case of hip replacement surgery, such devices include a cup which fits into the hip, and replaces the acetabulum, and a ball attached to a stem which fits into the femur and replaces the head of the femur. A cement is used to secure the prosthetic devices to the bone.
Currently, the cement used for such replacement is polymethylmethacrylate (PMMA), which requires the use of a catalyst for hardening of the cement. The catalyst, which is supplied in liquid form, must be mixed thoroughly with the methylmethacrylate monomer, and other dry components, to ensure a complete and even hardening of the cement. Typically, mixing of the components for between 0.5 to 2 minutes is required to obtain adequate mixing of the cement. After mixing, the cement is usually transferred to a delivery gun so that it can be applied to the areas required.
The time required for the cement to harden to a firm consistency is approximately 12-14 minutes, with complete hardening of the cement in about 24 hours. From the time the catalyst is mixed with the monomer the mixture begins to increase in viscosity until it eventually hardens. If there is a delay from the time the cement is mixed to the time it is delivered, as is common during a surgical procedure, the cement can become so viscous that it is very difficult or impossible to force from the delivery gun.
Currently, delivery guns are available that use a ratchet type mechanism for delivering the cement. These delivery guns are similar to that of a caulking gun for delivery of caulk to grout tiles. This ratchet type mechanism requires a great deal of strength to advance the ratchet to deliver viscous cement. Eventually the viscosity of the cement can become so great that delivery is not possible and the cement has to be discarded, necessitating the mixing of a new batch of cement. The need to mix a new batch of cement increases the length of the surgery. Also, most currently available delivery guns include metal parts and reusable components which must be cleaned and sterilized between uses.
It is desirable that a delivery gun is provided which is capable of delivering cement even when it has a high viscosity. It is also desirable that the delivery gun is disposable to minimize the clean-up required after a surgical procedure.